SU462154A1 - Induction logging probe - Google Patents

Description

In the circuit formed by the elements of the compensating coil probe, a current flows:

to

/about

to -

where ZK (Gk + / 0),) is the impedance of series-connected

GK and Lh.

Determining the voltage between the points of the SD circuit of the compensating coil as the difference jtH At / k, where At / is the voltage drop across the series-connected rk and Lit, we get:

UCD

(2)

CHZK + K)

From expressions (1) and (2) it can be seen that the phase of each of the two signals included in the measuring circuit oppositely is determined by the ratio of the impedances of the elements of the measuring and compensating coils of the probe.

2

Since in known probes the value is

2 (1 + and

differs from the value -, considered ZK-T-Rk

Signals cannot be compensated for by changing the position or number of turns of the compensating coil. The undercompensation voltage coincides in phase with the probe supply current and, therefore, with the useful signal from the surrounding rocks, i.e. it is a disturbance. Usually, this voltage is compensated by supplying the necessary signal in magnitude and phase to the probe circuit or the subsequent measuring circuit. However, due to temperature changes in the parameters of the probe coils (mainly Ki) in the course of operation in the well, the compensation position is disturbed and a change in the zero readings is observed, which leads to large measurement errors of high resistivity of the rocks.

These errors are also characteristic of probes with the number of rollers greater than three, including for the case when additional rollers are included in the exciting circuit of the probe.

In order to expand the range of measurements of the resistivity of rocks using induction logging multi-coded probes, the focusing and compensating coils are made identical in parameters and design, corresponding to the main coils, and are included in the exciting and measuring circuits to obtain the specified focusing parameters and degree

compensation e. d. the straight field of the probe is a part of the turns corresponding to the focusing and compensating coils. Such a solution provides a significant reduction in the voltage of undercompensation and automatic

compensation of the effect of changing the parameters of the probe coils during operation.

FIG. 3 shows a four-piece induction logging probe containing a main impulse roll 12, a focusing coil 13 in the excitation circuit, a focusing coil 14 in the measuring circuit and the main measurement roll 15. Since all the parameters of the coils 14 and 15 are the same, the contours formed by these coils and -resistance of losses, currents that coincide in phase flow. Therefore, the signals taken from the measuring coil of the probe 15 and from the divider formed by the focusing roller 14 can be

almost completely compensated. Similarly, the electromagnetic field from the coil 12 almost coincides in phase with the field from the included part of the turns of the coil 13,

Subject invention

Induction logging probe, consisting of main and additional focusing and compensating coils, respectively forming the exciter and measuring circuit of the probe, characterized in that, in order to expand the measurement range of the specific resistances of the rocks, focusing and compensating coils are high

identical in parameters and design to the main coils, and in the exciting and measuring circuits a part of the turns of the corresponding focusing and compensating catches are included.

Riga.1

not.2

Fig.Z